Linear particle accelerator with coast through shield

ABSTRACT

Charged particles injected into an energy beam, are accelerated by electric fields established in gaps between tubular electrodes through which the particles pass. Alternate gaps between the electrodes are enclosed by tubular shields through which the particles coast between the accelerating fields. The electrodes are charged by d.c. sources of opposite polarity.

llnited States Patent. 1191 Pollard et a1.

1451 Sept. 25, 1973 LINEAR PARTICLE ACCELERATOR WITH 3,478,241 11/1969Bliamptis et a1. 313/63 COAST THROUGH SHIELD 3,555,332 1/1971 Schroeder3,366,886 1/1968 Inventors: J ss L P lard, x 167, 3,387,176 6/1968Currie et a1 313/63 x Conyngham, Pa. 18219; Jesse 1. 3,406,349 10/1968Swain et a1. 313/63 X Pollard, 11, Box 7181, University, Miss 38677Primary ExaminerStanley D. Miller, Jr. [22] Filed; 10, 1970Att0rney-Clarence A. OBrien and Harvey B. 21 Appl. No.: 96,929 i 57ABSTRACT [52] US. Cl 328/227, 313/63, 313/83, 1

315/5.41, 315/5.42, 328/233, 328/256 Charged particles in ected mto anenergy beam, are ac- 51 Int. Cl o 23 00 ow" 29/00 celerated by electricfields established in gaps between [58] Field of Search 313/63, tubularelectrodes through which the Particles p 313/83; 328/233, 256, 227;315/541, 5.42 ternate gaps between the electrodes are enclosed bytubular shields through which the particles coast between 5 ReferencesCited the accelerating fields. The electrodes are charged by UNITEDSTATES PATENTS d.c. sources of opposite polarity.

3,218,562 11/1965 Sci-duke 328/233 8 Claims, 4 Drawing Figures /0 CLCHARGED \1 PARTICLE -r TARGET GENERATOR /2 m VELOCITY CONTROL POLARITYDC VOLT DC VOLT CONTROL SOURCE SOURCE uumDom JOmPZOu Jesse Pol/am JessePollard, ll

Patented Sept. 25, 1973 LINEAR PARTICLE ACCELERATOR WITH COAST THROUGHSHIELD This invention relates to the acceleration of charged particlesby energy fields established between electrodes of opposite polarity towhich direct current potentials are applied.

Charged particle accelerators employing spaced tubular electrodesbetween which accelerating energy fields are established, are well knownas disclosed for example in U. S. Pat. Nos. 2,683,216 and 3,366,836.Most of such particle accelerators employ electrical accelerating fieldsof the oscillating type with various arrangements for focussing ordirecting the fields to pro-,

duce the desired acceleration of particles such as electrons, protons,deuterons, ions, etc. In order to avoid the high power requirements andother problems inherent in the latter type of particle accelerator, ithas been proposed to utilize d.c. potentials forthe tubular elec-,trodes. Such accelerators require special means to prevent decelerationof the particles between the unidirectional accelerating fields. Otherdisadvantages replacing those associated with accelerators utilizingoscillating accelerating fields are however introduced. For example, aparticle accelerator utilizing direct current accelerating potentialsexclusively, are disclosed in US. Pat. No. 3,218,562. The latter patentdiscloses shielding tubes between the accelerating electrodes that areconnected to the source of potential and the accelerating fields aregenerated between the ends of theshielding tubes and the acceleratingelectrode rings. This field generating arrangement is relativelyinefficient and the structure associated therewith is difficult tooperationally align.

lt is therefore an important object of the. present invention to provideapparatus and a method for accelerating charged particles along linearpaths, arcuate orbits, curvilinear trajectories or combinations of theforegoing paths by avoiding the use of oscillating potentials for theaccelerating electrodes and without the field generating inefficienciesand structural instabilities associated with do. potential types ofparticle accelerators heretofore proposed.

In accordance with the present invention, a charged particle acceleratoris provided with tubular or annular electrodes to which do potentialsare applied for establishing accelerating electric energy fields in thegaps between adjacent electrodes and preventing deceleration of theparticles traveling from one accelerating field to another through theelectrodes by permitting the particles to coast through tubular shieldsisolated from the electordes and-the voltage supply means. The tubularshields are therefore positioned within alternate gaps between theelectrodes. Accordingly, the charged particles are only affected bythose fields in which they are accelerated in one direction therebypermitting the use of electrodes of fixed polarity.

These together with other objects and advantages which will becomesubsequently apparent reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing had to the accompanying drawings forming a part hereof, whereinlike numerals refer to like parts throughout, and in which:

FIG. I is a simplified electrical circuit diagram illustrating thesystem of the present invention.

FIG. 2 is a somewhat diagrammatic sectional view through a particleaccelerator constructed in accordance with the present invention.

FIGS. 3 and 4 show modified forms of tubular electrode arrangements ofthe accelerator, in longitudinal section.

Referring now to the drawings in detail, FIG. 1 illustrates a linearaccelerator generally denoted by reference numeral through which anenergy beam of charged particles 12 pass from a charged particlegenerator 14 to a target 16. The charged particles acquire a relativelyhigh velocity as a result of the energy withdrawn from energy fieldsestablished within the accelerator 10. Energy is supplied to theaccelerator from separate d.c. voltage sources 18 and 20 asdiagrammatically shown having output potentials of opposite polar--ities. These may be any even number of Van de Graaff generatorselectrically independent of each other. The polarity of the voltagesources 18 and 20 will depend upon the polarity of the charged particlesin the energy beam 12. The polarity of the charged particles from thegenerator 14 and the corresponding polarities of the voltage sources 18and 20 may therefore be reversed by any suitable polarity controlcomponent as shown in FIG. 1.

Also, the energy beam 12 may be either continuous or pulsed. If a pulsedbeam is utilized, energy in the form of ac. .current may be withdrawnfrom the beam. The particle velocity of the beam may be controlled atthe high energy end by use of a transformer 24 and a velocity controlcomponent 26 to which the transformer is connected. .Thus, full beampower can be maintained for prolonged periods of time without damage tothe target 16 by draining power from the beam through the transformer24.

As more clearly seen in FIG. 2, the particle accelerator comprises aplurality of spaced tubular electrodes or drift tubes 28-and 30 to whichpotentials of opposite I polarity are applied from the aforementionedvoltage sources 18 and 20. Thus, electric energy fields 32 areestablished in alternate gaps 34 between adjacent ends of the tubularelectrodes. In addition to the tubular electrodes, the acceleratingenergy fields 32 are separated by gaps 36 between the ends of adjacenttubular electrodes opposite the ends forming the accelerating gaps 34.Thus, with electrodes 28 being positively charged and electrodes 30being negatively charged, the energy fields 32 will acceleratenegatively charged particles 38 in a righthand direction as viewed inFIG. 2 along the path of the energy beam with which the tubularelectrodes are aligned. As hereinbefore indicated, the electrodes 28 and30 are charged with do potentials of fixed and opposite polarities. Thepolarities of the potentials applied to the electrodes 28 and 30 may ofcourse be reversed in order to accelerate positively charged particlesin the same direction.

In order to prevent deceleration of the particles passing through thegaps 36, tubular shields 40 are positioned in alignment with the tubularelectrodes and span the gaps 36 by projecting into or overlapping thetubular electrodes. These tubular shields 40 not only isolate theparticles 38 from the electric energy fields in gaps 36 but also isolatethem from the electrodes and the potentials applied thereto. Insulatingspacers 42 between the metallic electrodes end shields as shown may beutilized to minimize leakage energy losses resulting from any currentflow between electrodes of opposite polarity through the shields 40.Thus, charged particles accelerated by the energy fields 32, may coastthrough the tubular shields 40 without any loss in kinetic energy.

As a result of the arrangement hereinbefore described, the need forcostly apparatus in order to change the polarity of the electrodes iseliminated and the amount of power for sustaining operationsubstantially reduced.

Various configurations may be adopted for the tubular electrodes inorder to reduce the decelerating energy fields in alternate shieldedgaps. For example, the adjacent ends of the negative and positiveelectrodes 28 and 30' may be provided with bulbous formation 44 as shownin FIG. 3 to reduce fringing in gaps 36, with the shields 40 beingflared at ends 46. Alternatively, the adjacent ends 48 of electrodes 28"and 30 may be flared on either side of the decelerating gaps 36" asshown in FlG. 4. The accelerating gaps 34 and 34" in FIGS. 3 and 4 areformed between the smaller diameter ends of the electrodes.

The foregoing is considered as illustrative only of the principles ofthe invention. Further, since numerous modifications and changes willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation shown anddescribed, and accordingly all suitable modifications and equivalentsmay be resorted to, falling within the scope of the invention.

What is claimed as new is as follows:

1. Apparatus for accelerating charged particles along a predeterminedpath comprising a plurality of electrodes spaced from each other by gapsalong said path,

voltage supply means connected to said electrodes for establishingenergy fields unidirectionally accelerating said particles withinalternate ones of said gaps, coast means positioned within the other ofsaid gaps through which said particles pass between said acceleratingfields, and means for isolating the coast means from the electrodes andthe voltage supply means.

2. The combination of claim 1 wherein each of said electrodes iselongated in a direction along said path.

3. The combination of claim 1 wherein said coast means comprises tubularshields aligned with said electrodes along said path.

4. The combination of claim 3 wherein each of said electrodes iselongated in a direction along said path and has opposite ends, anassociated one of said energy fields extending from one of said oppositeends and one of the tubular shields extending from the other of saidends.

5. The combination of claim 3 wherein said tubular shields project intothe electrodes and are radially spaced therefrom by the isolating means.

6. The combination of claim 5 wherein the voltage supply means includesseparate sources of constant dc. voltage of opposite polarityrespectively connected to alternate ones of the electrodes.

7. The combination of claim 1 wherein the voltage supply means includesseparate sources of constant dc. voltage of opposite polarityrespectively connected to alternate ones of the electrodes.

8. The combination of claim 7 wherein said coast means comprises tubularshields aligned with said electrodes along said path.

1. Apparatus for accelerating charged particles along a predeterminedpath comprising a plurality of electrodes spaced from each other by gapsalong said path, voltage supply means connected to said electrodes forestablishing energy fields unidirectionally accelerating said particleswithin alternate ones of said gaps, coast means positioned within theother of said gaps through which said particles pass between saidaccelerating fields, and means for isolating the coast means from theelectrodes and the voltage supply means.
 2. The combination of claim 1wherein each of said electrodes is elongated in a direction along saidpath.
 3. The combination of claim 1 wherein said coast means comprisestubular shields aligned with said electrodes along said path.
 4. Thecombination of claim 3 wherein each of said electrodes is elongated in adirection along said path and has opposite ends, an associated one ofsaid energy fields extending from one of said opposite ends and one ofthe tubular shields extending from the other of said ends.
 5. Thecombination of claim 3 wherein said tubular shields project into theelectrodes and are radially spaced therefrom by the isolating means. 6.The combination of claim 5 wherein the voltage supply means includesseparate sources of constant d.c. voltage of opposite polarityrespectively connected to alternate ones of the electrodes.
 7. Thecombination of claim 1 wherein the voltage supply means includesseparate sources of constant d.c. voltage of opposite polarityrespectively connected to alternate ones of the electrodes.
 8. Thecombination of claim 7 wherein said coast means comprises tubularshields aligned with said electrodes along said path.